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This paper discusses part of a U.S. Bureau of Mines research effort to use electrochemical techniques to control sulfide flotation with the aim of developing new methods to process low-grade, complex domestic ores. The interactions between chalcocite and ethylxanthate (EtX?) have been studied in an electrochemical-microflotation cell containing a packed bed of the mineral as a working electrode. Spectrophotometric and electrochemical techniques have shown that in the potential range ?0.7 to 0 V (SCE) at a pH of 9.2 there are at least four distinct reactions: (1) a reaction of EtX? to form ethylperxanthate at reducing potentials near ?0.5 V; (2) a reaction of EtX? with soluble Cu(II) at the open circuit potential (?0.028 V); (3) an exchange reaction whereby EtX? displaces an oxidation product; and (4) a charge transfer oxidation reaction. The exchange and charge transfer oxidation reactions occur over the same potential range (?0.5 to ?0.1 V) and are both believed to produce cuprous xanthate and possibly cupric xanthate as an adsorbed hydrophobic species. Xanthate adsorbed at ?0.1 V can be desorbed as the ethylxanthate ion at more negative potentials. The flotation response of chalcocite is also shown to parallel closely the adsorption of EtX? by reactions 3 and 4 and the reduction of the adsorbed product during cathodic decreases in potential.